1. Field of the Invention
The present invention relates to an absorbent article suitable for absorbing menstrual blood and so on discharged from a woman's genital organ, more particularly, relates to an elongated absorbent article intended to cover the wearer's body from a vaginal opening to buttocks.
2. Description of the Related Art
Absorbent articles intended to absorb menstrual blood discharged from a woman's genital organ are typically constructed to include a liquid-permeable topsheet appearing on its skin surface, a liquid-impermeable backsheet appearing on its garment surface and a liquid absorbent layer disposed between the topsheet and the backsheet, and generally, they are worn with the backsheet adhered to an inner side of a groin piece of an undergarment through a pressure-sensitive adhesive layer.
In such an absorbent article, the function of certainly collecting menstrual blood applied to the skin surface is required so as to prevent lateral leakage of liquid and rearward leakage of liquid from the absorbent article.
Particularly in an absorbent article that is intended to be worn by a woman during menstruation while sleeping, required is not only prevention of lateral leakage of menstrual blood from the absorbent article but also prevention of leakage of menstrual blood trying to flow along the wearer's body toward the anus and the cleft of the buttocks or trying to flow along the skin surface of the absorbent article rearwardly. Accordingly, such an absorbent article for nighttime use is elongated more than absorbent articles for daytime use so that its skin surface can cover a large area from a mons pubis which is anterior to the vaginal opening to the buttocks which is posterior to the anus, as disclosed in Japanese Unexamined Patent Publication Nos. 2001-95842 and 2001-129018.
In such an elongated absorbent article, frequently employed is a topsheet with liquid passage holes uniformly distributed over a large area from a portion intended to face the vaginal opening to a portion intended to face the anus and the cleft of the buttocks. For example, the topsheet is a nonwoven fabric in which liquid passage holes are uniformly distributed over a large area or a resin film in which liquid passage holes are uniformly distributed.
In the nonwoven fabric, however, the surface frictional strength will be deteriorated due to a large number of liquid passage holes formed therein, so that when a large force is applied to the rear portion fitting in the cleft of the buttocks due to a change in posture such as rolling over, fibers may be fluffed around the liquid passage holes and breakage may possibly occur around the liquid passage holes.
In the case of using the resin film with the liquid passage holes formed therein, on the other hand, if the resin film is thin and soft, the topsheet will be easily wrinkled due to the change in posture at its portion which is in dose contact with the anus and the cleft of the buttocks. In the case where such a thin resin film is used, therefore, the resin film and an underlying layer are bonded together through a hot-melt adhesive so as to constrain the resin film with the underlying layer. However, the hot-melt adhesive may result in obstruction to permeation of menstrual blood from the topsheet to the underlying layer.
In the elongated absorbent article designed to cover a large area from the vaginal opening to the cleft of the buttocks, therefore, the front portion intended to face the vaginal opening and receive a large amount of menstrual blood at a time need be able to rapidly introduce the menstrual blood into the liquid absorbent layer, while the rear portion intended to face the anus and the cleft of the buttocks need not be rapid in liquid absorption but need be effective in retaining a small amount of menstrual blood so as to prevent leakage. In addition, the rear portion need be of sufficient durability or bonding strength to prevent fluffing and occurrence of breakage or inhibit occurrence of wrinkles due to compression in the cleft of the buttocks and friction against the buttocks. As understood from above, it is not the best to uniformly distribute the liquid passage holes over the topsheet covering different portions that differ from one another in required function.